Vibrations in rolling wheel assemblies (i.e. tyre+rim) are caused by several, different types of tyre imperfections, the most important being                Non-homogeneous mass distribution        Stiffness variations        Geometric variations        Radial and lateral run out        Eccentricity of the tyre        
Similar imperfections in the rim will also induce vibrations.
Vibrations in a truck or car wheel assembly due to imperfect tyres or rims cause vibrations which, apart from the discomfort to the driver and any passengers, can dramatically increase the tyre wear as well as mechanical wear. The present most common method for reducing wheel assembly derived vibration is still the attachment of metal weights to the tyre rim. However, this balancing technique, being of a static nature, cannot compensate for changes in load (i.e. deformation of the tyres), uneven wear of the tyres and the consequent changes in mass distribution, dirt collection on the rim, and the like. Consequently, balancing by means of metal weights must be repeated several times during the life time of a tyre.
The present invention is based on the fact that vibrations caused by imbalance in a wheel assembly can induce a motion in a liquid inside the tyre in a direction that will diminish the vibrations and the imbalance. However, to utilize this “vibrational pressure” to achieve balancing of a wheel assembly (i.e. that the gravitational centre is in the intersection between the rotational plane and the axis of rotation) is by no means trivial. If a mere free-flowing liquid such as water was introduced into a spinning tyre, any movement of this mass caused by a “vibrational pressure” would immediately be counteracted by the centrifugal force, which frequently exceeds 1000×g during normal driving, resulting in an oscillating movement of the liquid with no balancing effect.
These oscillations can be prevented/dampened sufficiently to achieve a balancing effect by using visco-elastic gels characterized by their critical yield stress and other rheological parameters.
U.S. Pat. No. 5,540,767, the content of which is hereby incorporated by reference, discloses visco-elastic tyre balancing compositions comprising (A) 80-95% w/w of an oil selected from i.a. polypropyleneglycol alkyl ethers, and (B) 4-15% w/w of a gel former selected from i.a. fumed silica having a BET surface in the range of from about 50 to about 400 m2/g.
The efficiency of these balancing gels can be demonstrated experimentally by measuring vertical accelerations on the spring leg of a front axle with its wheels running under load against a rotating drum.